The invention relates to a device for the automatic stepped, or incremental, cable length compensation of a Bowden cable system. Various embodiments of the invention are characterized by a simple construction, a reliable method of functioning, and the possibility of being made optionally from plastics or metal or a combination of the two materials.
Cable length compensation devices are generally used where cables are used as force-transferring members, and the cable lengthening, e.g., permanent stretching of the cable, which occurs under the action of the force needs to be compensated to maintain the functioning of the system. Such devices have had widespread use, particularly for so-called Bowden window regulators, for raising and lowering the side window panes of motor vehicles.
Common to many cable length compensation devices is the use of two parts movable relative to one another which are held under tension by a spring and carry out an adjusting movement when cable slack occurs. This adjusting movement corresponds in effect to a lengthening of the Bowden tube.
Furthermore it is known from DE 38 05 046 C2 to lock, by means of detent elements, the relative position of the two movable parts reached following the adjusting movement. A number of narrow successive detent elements which can drop one after the other behind the free end of the displaceable part guarantees a finely-stepped cable length compensation. This device is however not in a position to differentiate between a so-called genuine cable slack and an apparent cable slack which occurs in the event of high strain on a cable loop of a cable window regulator in the unstressed area of the cable loop. Thus considerable tensions can arise in the system which as a result of increased friction lead to a reduction in the degree of efficiency of the adjusting device and to accelerated wear and tear.
From EP 0 658 696 A1 a cable length compensation device is known for a Bowden window regulator which has a tubular part on the housing side and a part on the Bowden tube side which is movably mounted in the tubular part on the housing side. The part on the Bowden tube side supports both the Bowden tube on the one hand and a compression spring on the other hand, which presses the part on the Bowden tube side towards the Bowden tube. Several slits are formed evenly spread out over the circumference of the wall of the tubular part on the housing side so that detent teeth of an elastic split ring can pass through these slits to engage with counter teeth on the part on the Bowden tube side.
The expansion of the slits in the displacement direction is greater than the height of the detent teeth so that during displacement of the part on the Bowden tube side, first the detent teeth of the elastic split ring are entrained until they meet the boundary faces of the slits which act as stops. Only with a displacement movement beyond this is a relative movement caused between the elastic split ring and the part on the Bowden tube side, and thus a permanent, i.e., locked, setting movement, or rather, cable length compensation movement. The displacement movement is at least equal to the sum of the axial play of the elastic split ring in the slits of the part on the housing side and the division of the saw-tooth cogs of the part on the Bowden tube side. In each case the designated axial play for relaxing the tension of the system is provided by the supporting forces of the Bowden tube causing a restricted resetting movement of the displaceable part on the Bowden tube side until the detent teeth of the elastic split ring have reached the other stop of the slits.
The device described has however the drawback that the elastic split ring supported by the detent teeth can only be made of an elastic material owing to the high expanding capacity which is required for its assembly. Thus the forces which can be transferred by the elastic split ring are restricted.
A device which is very similar in construction and identical in its method of operation to that of EP 0 658 696 A1 is described in WO 96/25604. This device also consists of a part on the housing side and a sleeve-like part on the Bowden side which is displaceable therein and has external teeth in which the teeth of the locking element can engage. Also with this solution the locking element is mounted displaceably between two stops so that a movement play is formed with play allowance which provides the system with axial longitudinal play which prevents excessive tensioning of the adjustment device.
The drawback here however is that the inner arrangement of the detent element leads to the formation of comparatively small detent teeth. In conjunction with the locking element, which through necessity has to be made of plastics owing to the demands of elastic deformability, this device also can only be loaded to a restricted amount.